1. Field of the Invention
The present invention relates to a communication apparatus and a communication system, and particularly to a communication apparatus and a communication system which can maintain an excellent communication quality while minimizing a reduction in the number of usable frequency channels.
2. Description of Related Art
There is known a communication apparatus wirelessly communicating with another apparatus (which may be referred to as “an apparatus at the other end”) by utilizing FHSS (frequency-hopping spread spectrum) technology as a communication method. According to FHSS technology, a frequency of a carrier wave is changed or hopped in a cycle during a communication is made, that is, both a transmitting apparatus that sends out data and a receiving apparatus that receives the sent data identically change the frequency, or identically switch a channel to use among a plurality of channels, to keep a communication established.
More specifically, there is employed a FHSS method in which 79 channels are defined across a broadband of 2.4 GHz (2402-2480 MHz) with frequency intervals of 1 MHz, and, in the case of a cordless telephone, the channel switching is implemented at a rate of 100 times per second during a communication. When there is a radio wave of the same frequency in the air while the communication apparatus is making a communication, a problem occurs in the communication.
A technique to prevent such a problem is disclosed in JP-A-2002-198867 (see paragraph [0008]). That is, a data error rate is detected with respect to each of a plurality of frequency channels, and compared to a threshold. A frequency channel the data error rate of which is higher than the threshold is determined to be an interference channel which is a channel where interference occurs, and use of the interference channel is automatically ceased.
According to the technique where use of the frequency channel with a high data error rate is automatically ceased to decrease the number of usable channels, a shortage of usable frequency channels may occur depending on a value at which the threshold is set.